But 2017 could be on track to surpass it, with six killings so far in different states of the country: Cecilio Pineda, Ricardo Monlui, Miroslava Breach, Maximino Rodriguez, Valdez and now Adame.

Investigators have reported little progress in most of the cases.

Authorities arrested four suspects in the case of Rodriguez, a journalist for the blog Colectivo Pericu who was killed in Veracruz. But they have not identified who ordered the killing.

Two weeks ago, the government offered rewards of up to $85,000 each for leads in the cases of Pineda, Valdez, Rodriguez and Breach -- in what some branded an act of desperation.

Journalists and activists have protested the authorities' failure to bring journalists' killers to justice. The most recent protests were on June 15, one month after Valdez was gunned down in broad daylight.

Violence against journalists has surged since 2006, the year the Mexican government sent the army to fight the country's powerful narcotics cartels.

Since then, at least 100 journalists have been killed, more than 20 have gone missing and more than 200 report surviving attacks by drug gang thugs.

The violence is part of a wave of bloodshed in Mexico over the same period that has left more than 200,000 people dead or missing.